1. Field of the Invention
The present invention relates to a microactuator and, more particularly, to a microactuator using a piezoelectric material and a method of manufacturing the same.
2. Related Background Art
In recent years, actuators for moving small objects to arbitrary positions or directions are important along with the developments of automation and high-precision measurement techniques. Strong demand has also arisen for compact actuators along with the above developments.
A piezoactutor consisting of a material having a piezoelectric effect used in a scanning tunneling microscope (STM) is a typical example of a high-precision moving or positioning drive mechanism. The STM measures a tunneling current between the surface of a conductive serving as a sample and a probe having a very sharp distal end. A drive mechanism for this STM must bring the probe to a position several tens of angstroms or less from the surface of the conductive and must therefore have drive precision on the order of angstroms as moving or positioning precision of the probe. Conventional bulk type piezoactuators include a tripod type piezoactuator (G. Binnig et al., IBM Technical Disclosure Bulletin, vol. 27, no. 10B, 1985, pp. 5976-5977) and a tube type piezoactuator (G. Binnig et al., "Single-tube three-dimensional scanner for scanning tunneling microscopy", Rev. Sci. Instrum., 57(8), 1986, pp. 1688-1689). A piezoelectric material serving as a constituent element is generally formed, starting with blending of raw materials and performing mixing/pulverization (crush), calcination, pulverization (crush), binder mixing, molding, sintering, working, electrode formation, and polarization (Tadashi Shiozaki ed., "Manufacturing and Applications of Piezoelectric Materials", CMC, 1985, pp. 19-21). The bulk type piezoactuator has limitations on the manufacturing method and working precision because it is manufactured by polishing, cutting, and the like.
A micromechanics technique using a silicon planar process has received a great deal of attention as a technique for manufacturing a compact actuator. A variety of actuators are proposed using this technique. Main state-of-the-art microactuators utilize driving force such as the piezoelectric effect of a piezoelectric thin film and an electrostatic force. Of all the microactuators, the microactuator utilizing the piezoelectric effect does not require a clearance required for the electrostatic force and can obtain desired deformation in a self-standing manner. An example is a piezoelectric bimorth actuator (S. Akamine et al., "Microfabricated Scanning Tunneling Microscope" IEEE ELECTRON DEVICE LETTERS, VOL. 10, NO. 11, pp. 490-492 (1989)).
In microfabrication mainly using the silicon planar process, the degree of freedom in design is limited because the two-dimensional surface of a substrate is processed. This is because it is difficult to form a thick layer having a thickness of several microns to several tens of microns so as to deposite a thin film of an actuator material such as a piezoelectric material.
As a method for improving the degree of freedom in the process, an LIGA technique (Lithographie, Galvanoformung, Abformung) using synchrotron radiation light is proposed by W. Ehrfeld et al. of Kernforshungszentrum Karlsruhe (IEEE Solid-State Sensor and Actuator Workshop, Hilton Head. S.C., 1988, Technical Digest pp. 1-4). In addition, a technique capable of manufacturing a freer three-dimensional structure by forming a sacrificial layer in the LIGA technique is also proposed (H. Guckel et al., "Fabrication and testing of the planar magnetic micromotor", J. Micromech. Microeng., 1. 1991. pp. 135-138). Structures proposed as actuators using the LIGA technique require energy fields such as an electrostatic force and a magnetic force and must use drive means with a clearance. An independent operation obtained in use of the piezoelectric effect cannot be achieved.